This invention relates to electrical transformers. More particularly, this invention relates to a method and apparatus for making a jointed magnetic core from amorphous metal ribbons.
Several methods and apparatus have been proposed for manufacturing jointed magnetic cores. However, these methods and apparatus often require specialized hardware for holding fully parted strips and therefore have proven unnecessarily expensive and complicated.
Current methods for constructing a jointed magnetic core from fully parted amorphous metal strips utilize belt winders and specialized holding devices to secure fully parted strips during construction of the core. For example, U.S. Pat. No. 3,049,793 (""793) discloses using a belt nester in a process wherein cut lengths of conventional metal are wrapped or nested about a rotating arbor by a continuous belt. U.S. Pat. Nos. 5,230,139 (""139 Patent) and U.S. Pat. No. 5,315,754 (""754 Patent), extend upon the belt nester concept to disclose a method of producing a transformer core using amorphous metal strips instead of conventional silicon-iron materials. While the usual thickness of silicon-iron materials is about 0.15 to about 0.3 millimeter, amorphous alloys are much thinner, typically about 0.025 millimeter. Because amorphous alloys are thinner, they slide easily and are less rigid than conventional silicon-iron materials. In order to deal with the problems presented by the lack of rigidity of the amorphous metal, the ""139 Patent and ""754 Patent disclose special steering and flattening devices that have been added to the basic belt nester configuration. Further, manual and automatic optical methods are disclosed for maintaining a correct lap in the joint area. Thus, these known methods and apparatus employ complicated and specialized components for holding the strips in place and maintaining the correct lap.
A second method of making an amorphous jointed core which similarly requires using complicated clamps and holding devices, involves wrapping cut strips around a non-rotating mandrel. For example, U.S. Pat. No. 5,093,981 (""981 Patent) discloses a process wherein cut strips are transported to and wrapped around a non-rotating arbor. After wrapping, the strips are secured with specialized clamp and belt holding devices. Additional strips are added until the core reaches the desired size. U.S. Pat. No. 5,309,627 (""627 Patent) discloses a method of making a non-circular cross section core by wrapping individual packets of core strips around a stationary mandrel. The method disclosed in the ""627 Patent requires multiple rollers and pressure pads to wrap and hold the cut strips around the mandrel. U.S. Pat. No. 5,261,152 (""152 Patent) discloses a method for manufacturing an amorphous magnetic core by supplying cut sheets which are wrapped around a rectangular mandrel. The cut sheets are either manually or automatically fastened with tape while being held in position with pressers. Thus, the ""152 Patent, ""627 Patent, and ""981 Patent require considerable handling of the cut strips as well as complex clamping and holding equipment.
Another method of making a jointed core is disclosed in U.S. Pat. No. 2,657,456 (""456 Patent). The method disclosed in the ""456 Patent creates a joint by weakening each layer of the core at predetermined positions and thereafter mechanically breaking the weakened areas to create a joint in the core. Although the method of the ""456 patent was intended for the manufacture of cores from conventional silicon-iron materials, it is conceivable that the method of the ""456 Patent could be applied to amorphous materials as well. However, there are several difficulties that could be expected from using the method of the ""456 Patent with amorphous materials. An amorphous core has thousands of layers, and therefore would require thousands of the operations disclosed in the ""456 Patent to create the weakened areas. It is common when processing amorphous metals to process multiple strips together to reduce the number of operations required. This would make this method much more feasible with amorphous metals. Also, when cutting a strip of amorphous metal to weaken an area for later breaking, an undesirable burr on the cut edge often occurs. The presence of this burr creates an undesirable lack of tightness in the wound core. Furthermore, the preferred joint for use with amorphous metals is a fully or almost fully lapped joint. Such a joint may not be constructed with the disclosed method without adding additional steps such as relacing around a smaller mandrel, or by stopping the process to cut and overlap the core strip. Thus, the method disclosed in the ""456 Patent is not optimal for making an amorphous metal jointed core.
Therefore, an object of the present invention is to provide a method and apparatus for producing an amorphous metal distributed gap core without the use of a belt nester and without requiring elaborate clamping and holding devices to secure the fully parted strips. It is a further object to provide a method that allows the automatic cutting and positioning of strips to ensure proper joint location without requiring operator attention to the process.
The above objects have been met in accordance ; the present invention by providing a method for making a transformer core from amorphous metal strip using a mandrel, wherein the transformer core has a joint region. The method comprises the following steps: wrapping fully parted metal strip around the mandrel, wherein the strip has a longitudinal edge and a transverse edge; and wrapping amorphous metal ribbon over the fully parted metal strip so as to secure the fully parted metal strip to the mandrel, wherein the amorphous metal ribbon has a weakened area located in the transformer joint region. The method may also comprise the step of interweaving a plurality of strips with the ribbon around the mandrel so as to form layers of strips and layers of ribbon around the mandrel and thereby secure the plurality of strips to the mandrel with the ribbon, wherein each of the layers of ribbon has a weakened area in the joint region of the core.
The method may further comprise the step of fully parting the ribbon in the joint region. The core may be annealed before or after parting the ribbon in the joint region.
The amorphous metal ribbon may comprise one or more ribbons that have been spliced together. Alternatively, the amorphous metal ribbon may comprise a plurality of ribbons.
The fully parted metal strip may comprise one or more groups of cut metal ribbon. The longitudinal edges of the cut metal ribbon in each group are substantially aligned and the transverse edges in each group are substantially aligned. The strip may comprise a plurality of groups of cut metal ribbon, wherein the longitudinal edges of the cut metal ribbon in each group are substantially aligned and the transverse edges of the cut metal ribbon in each group are substantially aligned, while the longitudinal edges of adjacent groups are substantially aligned and transverse edges of adjacent groups are staggered with respect to each other.
The metal ribbon may be weakened in predetermined areas by partially cutting the ribbon. The ribbon may be cut from each longitudinal edge while leaving an uncut portion in the center of the ribbon.
According to another aspect of the invention there is disclosed a system for wrapping transformer cores from amorphous metal strips and a ribbon of amorphous metal ribbon having weakened areas. The system comprises the following items: a strip supply mechanism for providing cut strips of amorphous metal; a ribbon supply mechanism for providing a ribbon of amorphous metal; a rotating winding mechanism situated relative to the strip supply mechanism and the ribbon supply mechanism so that as the winding mechanism rotates, the ribbon and the cut strips are fed onto the mandrel and interwoven with each other so as to form layers of strips and layers of ribbon around the winding mechanism, thereby securing the cut strips to the winding mechanism with the ribbon.
The strip supply mechanism may comprise a moveable belt and clamp, wherein the clamp secures the strip to the moveable belt while the strip is transported to the winding mechanism and the clamp releases the strip when the strip is wound onto the winding mechanism.
The ribbon supply mechanism may comprise the following items: a ribbon payoff from which the ribbon is unspooled; an encoder for tracking the length of ribbon and determining the appropriate location to weaken the ribbon; and a weakening device for weakening the ribbon in the appropriate locations as determined by said encoder. The ribbon supply mechanism may comprise one or more amorphous metal ribbons having weakened areas at predetermined locations.
The winding mechanism may comprise the following items: a mandrel upon which is wound cut strip and the ribbon; and a positioning device operably connected to z he mandrel for adjusting the location of the mandrel as the strip and ribbon are wound onto the mandrel so as to compensate for the increased build of the wound strip and ribbon. The winding mechanism may comprise a movable pressure plate which can be made to come in contact with the ribbon being wound onto the mandrel so as to add tension to the ribbon.
According to another aspect of the invention there is disclosed a machine for wrapping a transformer core having a joint region. The machine comprises the following items: a means for providing amorphous metal fully cut strips; a means for providing one or more amorphous metal ribbon; a means for weakening the amorphous metal ribbon at predetermined locations; and a means for wrapping the strips and the ribbons around a mandrel such that the predetermined locations are in the joint region of the core.
The means for providing amorphous metal fully cut strips may include a transport means for moving amorphous metal fully cut strips to the mandrel. The transport means may comprise one or more amorphous metal ribbons having weakened areas at predetermined locations. The transport means may alternatively comprise a moveable belt and a clamp, wherein the clamp secures the strip to the moveable belt while the strip is transported to the wrapping means and the clamp releases the strip when the strip is wound onto the wrapping means.
The means for wrapping may comprise the following items: a mandrel upon which is wound cut strip and the ribbon; a backplate affixed to the mandrel for guiding the cut strip and ribbon onto the mandrel; and a positioning device operably connected to the mandrel for adjusting the location of the mandrel as the strip and ribbon are wound onto the mandrel so as to compensate for the increased build of the wound strip and ribbon. The wrapping means may further comprise a movable pressure plate which can be made to come in contact with the ribbon being wound onto the mandrel so as to add tension to the ribbon. The machine may have a rotating mandrel.
According to another aspect of the invention there is disclosed a distributed gap core comprising fully parted amorphous metal strips interwoven with one or more non-parted amorphous metal ribbons with weakened areas at predetermined locations within the joint region.
According to another aspect, there is disclosed a distributed gap core comprising fully parted amorphous metal strips interwoven with one or more amorphous metal ribbons with weakened areas at predetermined locations within the joint region, wherein the ribbons have been fully parted after winding into a core. The strips may comprise one or more groups of cut ribbon having substantially aligned longitudinal edges and substantially aligned transverse edges. Alternatively, the strips may comprise groups of cut ribbon having substantially aligned longitudinal edges and substantially aligned transverse edges, wherein adjacent groups have substantially aligned longitudinal edges and transverse edges which are staggered with respect to each other. The core may be annealed before or after the ribbons are parted.